Action of Neutral Salts. 



129 



186 (1364) 



The action of neutral salts on the osmotic pressure and other 



qualities of gelatin. 



By Jacques Loeb. 



[From The Rocekfeller Institute for Medical Research.] 



Hofmeister and his followers had stated that chiefly the anion 

 of a neutral salt influenced the swelling of gelatin, while the cation 

 had little or no effect. Later on it was stated by colloid chemists 

 that the action of neutral salts on the physical qualities of colloids 

 is the algebraic sum of the opposite action of the two oppositely 

 charged ions of the salt used. Neither of the two statements is 

 correct. The former authors were led to erroneous conclusions 

 by the fact that they always investigated the effect of the salt on 

 the protein in the presence of a high concentration of the salt. 

 Now it happens that the presence of the salt suppresses part of 

 those physical changes in the behavior of the colloids which are 

 caused by the action of the salt upon the protein. The writer 

 avoided this error by using either finely pulverized gelatin or dried 

 pig's bladder, and by washing away the excess of salt after the 

 latter had had a chance to act on the gelatin. 



Contrary to the statement current in colloid chemistry, the 

 writer found by this method that (as long as the salts are not used 

 in excessive concentrations) only one of the two ions of the salts 

 acts upon the protein. Common gelatin, as well as gelatin pre- 

 viously treated by a base, is influenced exclusively by the cation 

 of the neutral salt used, while gelatin which had previously been 

 treated with an acid is only influenced by the anion of the salt 

 used. In the former case, treatment of gelatin with salts 

 with monovalent cation (NaCl, Na 2 S04, etc.) causes an increase 

 in swelling, in viscosity, in the quantity of alcohol required 

 for precipitation, and in osmotic pressure of the gelatin, after the 

 excess of salt is washed away ; while when the cation of the salt used 

 is bivalent no such increase is observed. When gelatin, previously 

 treated with an acid, is treated with a neutral salt, only the anion 

 of the latter acts upon the gelatin ; the salts with monovalent anion 



